In the production and utilization of different types of integrated circuit (IC) chips and particularly with respect to dynamic random access memories (hereinafter DRAMs) it is sometimes desirable to have a single chip configuration capable of operating in different modes; i.e. for one particular application it might be desirable that the DRAM operate in a Page mode (e.g. a mode where CAS is used to trap addresses) and, another mode where the DRAM operates in a Static Column mode in such a case the write pulse can trap addresses). It is possible to design two different inputs to the chip so that depending upon the input, the chip will operate in either a Page mode or a Static Column mode. However, this requires two separate chips and two separate part numbers and, thus, a common chip cannot be used to operate in both modes. Yet for many reasons it may be desirable to have the same chip operate in two or more different modes. An example of operation of a DRAM is described in a third mode in U.S. Pat. No. 4,845,664, "On-Chip Bit Reordering Structure" (assigned to IBM), the teachings of which are incorporated herein by reference.
It is generally desirable to provide multiple operating modes utilizing a single chip configuration, so as to not require separate chips and part numbers. Conventionally, memory chips are operated in default modes. If different modes are needed, different chips must be provided. A single chip, able to operate in multiple modes, saves manufacturing and inventory costs. Manufacturing unique integrated circuits requires multiple sets of masks, test specifications, assembly specifications and inventory control documents which all add to the cost of the chip.
There have been prior attempts at providing dual state mode recognition; for example, U.S. Pat. No. 4,159,541 to Ward, et al. shows a mode selector which selects a "read" or "write" operation. However, this patent does not show selection between two different types of operating modes of a DRAM and, especially, wherein there is a third mode which is actuated if the mode switches during certain conditions and is reset to the original mode.